. >> it's so hard to grasp the fact that we are in the 21st century in the united states of america and you're still seeing this-- a fully functional ecosystem, phenomenal pulses of life moving up these rivers. >> wild fish are important because they are beautiful. it's a beautiful species and they are a miracle of nature. but they're important because they are also the food source for everything from bears to caddisflies to eagles to killer whales. i mean, that's what feeds the food webs of the north pacific, wild salmon protein, pumped out of the ocean up into the rivers, delivered almost perfectly to every corner of the watershed. >> narrator: bristol bay's great sockeye salmon run is concentrated in several major river systems. each year, millions of fish swim up rivers like the nushagak or the kvichak to get to their spawning streams. it's here, north of lake iliamna, between two branches of that pristine watershed, that an extraordinary discovery has been made. for decades, several mining companies have been exploring the area, drilling core samples and mapping an area called the